1. Field of the Invention
This invention relates generally to paper manufactures and more specifically to box machines for folding paperboard blanks.
2. Description of the Prior Art
Folding and sealing apparatus is generally known in the corrugated paperboard industry, such machines being known as folder-gluers. These machines usually fold advancing blanks by means of moving belts or rotating rods or levers. Although many patents exist that show such machines, Lopez U.S. Pat. No. 3,122,069 is considered exemplary of the belt type and Spiess U.S. Pat. No. 3,240,185 is considered exemplary of the rod type.
In known folder-gluers, corrugated paperboard blanks, having folding or score lines and slots therein forming the dimensions of an erected carton, are advanced through the machine which folds the outermost panels defined by the score lines into overlapping relationship. Glue is applied along the outer edge of one panel so that it becomes bonded to an outer edge of the other panel thereby forming a flat tubular carton. Stacks of such blanks are shipped to the customer who then erects them, either manually or by machine, fills them with his goods, seals them and then ships the goods to the consumer.
The blanks, prior to folding, may be fed directly into the folder-gluer by a special feeding unit or the blanks may be fed directly from a printer-slotter machine which prints, scores, and slots the blanks. The folding elements of the folder, whether of the belt or rod type, are positioned across the width of the blank, that is, transverse to the direction of blank travel, so as to be substantially aligned with the score lines about which the blanks are to be folded.
Certain difficulties arise in the use of known folding apparatus such as the folded panels not being folded squarely with the non-folded panels. Another difficulty is that blanks having relatively large panel portions and long slots in the blanks often tear in the directon of the slots during the folding operation. This often occurs in blanks of low quality and is produced mainly by friction and bending forces along the grooves.